1. Field of the Invention
This invention relates to an optical recording medium especially suitable for application to a phase change versatile optical disc available for repetitive recording and erasure.
2. Description of the Related Art
In recent data recording technologies, researches are being developed regarding optical recording systems. Optical recording systems can record and reproduce information signals without contacting a recording medium, and can attain higher recording densities as ten times or more as that those of magnetic recording systems. Additionally, optical recording systems have a number of advantages, including the availability for use with any type of memory such as reproduction-exclusive type, additional recording type and rewritable type. Thus, the optical recording systems are expected to be widely usable in industrial purposes and home-base purposes as a recording system that enables realization of inexpensive, large-capacity files.
Among those optical recording systems, optical magnetic discs and phase change versatile optical discs, for example, cope with rewritable memory modes. Optical magnetic discs are configured to locally heat a recording film made of a magnetic material to or above a Curie point or a temperature compensation point, thereby to decrease the coercive force of the recording medium, then apply an external recording magnetic field, thereby to change the magnetic orientation of the recording medium, and record information signals, or magnetically read out information signals. On the other hand, phase change versatile optical discs includes a recording film made of a phase change versatile material in which changes between a crystalline state and an amorphous state reversibly occur, and are configured to heat the recording film by irradiation of laser light, for example, thereby cause a change in phase in the recording film to record/erase information, or optically read out information signals.
As a conventional phase change versatile disc, CD-RW (Compact Disc-ReWritable) is known and being widely spread. The format of CD-RW is shown below.
Wavelength of light: 780 nm
Numerical aperture of the optical system lens:
Capacity: 650 MB
Track pitch: 1.6 xcexcm
Reflectance: 15 through 25%
Modulation: 55 through 70%
Resolution: 45 through 60%
Linear velocity: 1.2 through 4.8 m/s (equal to four-times velocity)
Repeatable recording frequency: 1000 times or more.
In order to realize such a phase change versatile optical disc under that regulation (specifically, CD-RW), AgInSbTe-series materials are used as phase change versatile materials, and Alxe2x80x94Ti alloys and Alxe2x80x94Cr alloys are used as materials of reflecting films.
The conventional phase change versatile discs improvement in recording speed and reproducing speed are demanded. When an improvement of the linear velocity is tried toward realization of high-speed recording and high-speed reproduction, the following problem will occur. That is, recording or reproduction of information signals at a higher linear velocity than the conventional maximum linear velocity (linear velocity of about 4.8m/s (four-times velocity)) will invite deterioration of jitters and decrease of the modulation. Therefore, practically acceptable recording characteristics could not be obtained.
It is therefore an object of the invention to provide an optical recording medium capable of preventing deterioration of jitters and a decrease of the modulation even at a linear velocity higher than 4.8 m/s, and thereby ensuring practically acceptable recording characteristics.
According to the first aspect of the invention, there is provided an optical recording medium comprising:
a substrate having ridge-and-furrow groove tracks on one major surface thereof; and
a first dielectric film, phase change versatile recording film, second dielectric film and reflection film that are sequentially stacked on the one major surface of the substrate,
the phase change versatile recording film being made of a GeInSbTe alloy material, and the reflection film being made of an AgPdCu alloy material,
in the GeInSbTe alloy material forming the phase change versatile recording film, content of Ge being in the range from 1 weight % to 6 weight %, content of In being in the range from 2 weight % to 6 weight %, and ratio of Sb relative to Te being in the range of 2.2 times to 3.0 times, and in the AgPdCu alloy material forming the reflection film, content of Pd being in the range of 0.9 weight % to 1.5 weight %, and content of Cu being in the range of 0.9 weight % to 1.1 weight %,
depth of the furrow on the groove tracks being in the range from 40 nm to 50 nm, and distance between two adjacent boundaries at opposite sides of the furrow being in the range of 0.40 xcexcm to 0.65 xcexcm,
thickness of the first dielectric film being in the range of 75 nm to 95 nm, thickness of the phase change versatile recording film being in the range of 12 nm to 18 nm, thickness of the second dielectric film being in the range of 20 nm to 28 nm, and thickness of the reflection film being in the range of 60 nm to 140 nm.
According to the second aspect of the invention, there is provided an optical recording medium comprising:
a substrate having ridge-and-furrow groove tracks on one major surface thereof; and
a first dielectric film, phase change versatile recording film, second dielectric film and reflection film that are sequentially stacked on the major surface of the substrate,
the phase change versatile recording film being made of a GeInSbTe alloy material, and the reflection film being made of an AlCu alloy material,
in the GeInSbTe alloy material forming the phase change versatile recording film, content of Ge being in the range from 1 weight % to 6 weight %, content of In being in the range from 2 weight % to 6 weight %, and ratio of Sb relative to Te being in the range of 2.2 times to 3.0 times, and in the AlCu alloy material forming the reflection film, content of Cu being not more than 1.5 weight %,
depth of the furrow on the groove tracks being in the range from 40 nm to 50 nm, and distance between two adjacent boundaries at opposite sides of the furrow being in the range of 0.40 xcexcm to 0.65 xcexcm,
thickness of the first dielectric film being in the range of 75 nm to 95 nm, thickness of the phase change versatile recording film being in the range of 12 nm to 18 nm, thickness of the second dielectric film being in the range of 20 nm to 28 nm, and thickness of the reflection film being in the range of 60 nm to 140 nm.
In the present invention, wavelength of light irradiated onto the phase change versatile recording film of the optical recording medium upon recording or erasing information signal on or from the optical recording medium is typically selected from the range of 775 nm to 795 nm, approximately, and more specifically, it is about 780 nm, for example.
In the present invention, numerical aperture of the lens in the optical system used upon recording or erasing information signals on or from the optical recording medium is typically in the range from 0.49 to 0.51, and numerical aperture of the lens in the optical system used upon reproducing information signals is typically in the range from 0.44 to 0.46. More specifically, numerical aperture of the lens in the optical system used upon recording or erasing information signals on or from the optical recording medium is approximately 0.5, and numerical aperture of the lens in the optical system used upon reproducing information signals is approximately 0.45.
In the present invention, the recording linear density in the optical recording medium is typically 0.59 xcexcm per bit.
In the present invention, ratio of Sb relative to Te in the GeInSbTe alloy material forming the phase change versatile recording film is preferably 2.2 times to 2.8 times.
In the present invention, width between two adjacent boundaries at opposite sides of a furrow is preferably in the range from 0.52 xcexcm to 0.65 xcexcm.
In the present invention, the first dielectric film is made of a material with a low absorptance to laser light of the optical system used upon recording/reproduction to the optical recording medium. Preferably, a material having a value of extinction coefficient k not higher than 0.3 is used as the material of the first dielectric film.
In the present invention, the second dielectric film is made of a material with a low absorptance to laser light of the optical system used upon recording/reproduction of the optical recording medium. Preferably, a material having a value of extinction coefficient k not higher than 0.3 is used as the material of the first dielectric film.
In the present invention, the optical recording medium is a rewritable optical recording medium using a phase change versatile material as the recording film. Specifically, it may be CD-RW (Compact Disc ReWritable).
According to the optical recording medium having the above-summarized configuration according to the invention, the phase change versatile recording film in the optical recording medium is made of a GeInSbTe alloy material; the reflection film is made of an AgPdCu alloy material or AlCu alloy material; the GeInSbTe alloy material forming the phase change versatile recording film contains Ge in the range from 1 weight % to 6 weight %, In in the range from 2 weight % to 6 weight %, and Sb in the range from 2.2 times to 3.0 times of Te; in case of using the AgPdCu alloy material to form the reflection film, it contains Pd in the range from 0.9 weight % to 1.5 weight % and Cu in the range from 0.9 weight % to 1.1 weight %; in case of using the AlCu alloy material to form the reflection film, it contains Cu not more than 1.5 weight %; depth of each groove of the groove tracks on the major surface of the substrate is in the range from 40 nm to 50 nm; distance between two boundaries, among boundaries between lands and grooves of the groove tracks, is in the range from 0.40 xcexcm to 0.65 xcexcm; thickness of the first dielectric film is in the range from 75 nm to 95 nm; thickness of the phase change versatile recording film is in the range from 12 nm to 18 nm; thickness of the second dielectric film is in the range from 20 nm to 28 nm, and thickness of the reflection film is in the range from 60 nm to 140 nm. This configuration can prevent deterioration of jitters and a decrease of the modulation even when the linear velocity is increased upon recording and/or erasing information signals, and thereby ensures sufficient recording characteristics in the optical recording medium.